FR2523279A1 - FIXED PRISMATIC REFRACTOR FOR CONCENTRATING SOLAR ENERGY ON A COLLECTING SURFACE - Google Patents

Abstract

THE INVENTION CONCERNS A REFRACTOR, MADE OF A TRANSPARENT MATERIAL DESIGNED TO REMAIN IN A FIXED POSITION OVER TIME, WHICH INCLUDES AFOCAL STRUCTURAL ELEMENTS, SUCH AS STRAIGHT PRISMS, OF APPROPRIATE DIMENSIONS, WHICH ARE ARRANGED ASYMMETRICALLY IN RELATION TO A LINE OF JUNCTION Q, SO AS TO OBTAIN A SOLAR ENERGY CONCENTRATION RATIO C GREATER OR EQUAL TO 2.6 ON AN APPROPRIATE COLLECTING SURFACE PMC, DURING THE PERIOD WHICH GOES FROM 8 AM TO 4 PM. ADVANTAGEOUSLY, THE REFRACTOR R HAS, IN ITS LOWER PART, 42 PRISMS HAVING A HEIGHT E OF AT LEAST 3 MM AND A WIDTH 1 OF AT LEAST 4 MM AND, IN ITS UPPER PART, 9 PRISMS OF THE SAME HEIGHT BUT WIDTH IS AT LEAST 6.5 MM, THE COLLECTING SURFACE BEING LOCATED AT A DISTANCE OF APPROXIMATELY 350 MM FROM THE FLAT FACE OF THE REFRACTOR.

Description

The present invention relates to a refractor

  placed with several straight prisms each of which has appropriate dimensions and is made of a transparent material, in which said prisms are arranged to form a structure comprising a flat face and a serrated or crenellated face. To obtain suitable refractors to concentrate

  solar energy, we have used in the past the capacity of

  ne lens with a "Presnel lens" type profile for

  focus a beam of parallel rays towards the point fo-

  cal Refractors using such lenses are already known in the art; these refractors are either mounted

  on mechanisms that follow the apparent displacement of the so-

  leil, either fixed but, in the latter case, they are coupled

  to appropriate elements that simulate such mechanisms.

  The applications of these refractors are relatively

  expensive and are of a complex implementation.

  An earlier patent application by the Applicant describes a refractor composed of elements of the "Fresnel lens" type, but which is asymmetrical, that is to say that it has no

  plus a single focus You can get an ap-

  valuable solar energy transmitted using this re-

  fractor, although its position remains fixed over time.

  Therefore, one can get well devices

  simpler and easier to use.

  The realization of the above-mentioned refractor parts

  however, there are still manufacturing and

  results, therefore, in relatively high costs.

  Consequently, the Applicant has carried out other

  research and experience and discovered a new type of research

  original fractor which is the subject of the present invention.

  Such a refractor can be considered to be

  evolutionary in the sense that it can be made both easily and at relatively low cost, and from a material

  any solid transparent; it is also possible to

  use, for example, any known type of equipment

  continuous production of window glass.

  Furthermore, when using a device such as this-

  him of the present invention, it is more easily

  screw the crenel_e face To the rf-reactor of suitable layers with high reflective power in order to minimize the dispersion towards the outside of the energy reflected by the user device, the reflector of which according to the invention forms the cover In the refractors known up to now in the art, it has turned out that the deposition of such reflective layers was, on the contrary, less easy due to

the shape of the surface.

  It should also be noted that the refractor is

  lon the invention can be used as a modular element for

  larger collecting areas.

  In fact, multiple combinations can be imagined.

  born and it is obvious that to maintain the relationship of con-

  centration associated with the modular element, there should be

  as many areas of the collecting surface as will be used

modular elements.

  Other characteristics and advantages of the invention

  will emerge from the description which follows, given as

  non-limiting example and with reference to the accompanying drawings in which: FIG. 1 is a sectional view accompanied by a partial plan view of the refractor according to the invention; Fig la is a view, on a larger scale for

  facilitate understanding, from a single right prism of the

fractor;

  Fig 2 is a schematic view of the refractor, used

  read to explain the definition of focal length;

  Fig 3 is, similarly, a schematic representation

  as the refractor of Fig 1, shown in a provision

  tion suitable for receiving solar energy on its flat face; FIG. 4 is a graph on which the curve of the concentration ratio of solar energy has been plotted as a function of the distance between the collecting surface and the refractor;

  Fig. 5 represents the images of the transmissible sun

  its by the refractor to the maximum concentration plan from 8 am to 12 pm; Fig 6 is a graph on which we have drawn the

  outermost rays refracted by the elements taken

  matics, rays used to determine the distance between

  the maximum concentration plan and the refractor.

  As can be seen in the drawing, the present invention

  tion relates to a refracting device R which remains in a fixed position over time and which is obtained by using various afocal structural elements, namely prisms

  rights p which are arranged side by side c 8 te and which are suitable-

  dimensioned to obtain a con-

  centering C az 2.60 during a significant part of the day-

born.

  The term C-concentration is understood to mean in the pre-

  In this case, the ratio between the width L of the refractor and the

  width LI of the surface lit by the sun on an over-

  collecting face during the part of the day considered.

  The distinctive feature of the device according to

  the invention is that there is a plane in the half space if-

  killed on the other side of the incidence plane in which a report

  port of concentration C 2 / 2.6, as defined above, can be reached for a period of up to eight hours, depending on the season This plan is defined as

  maximum concentration plan Pmc (see Fig 6).

  Outside the maximum concentration plane Pmc, solar energy can be captured in any plane located at any distance d from the flat surface of the refractor R. Naturally, the concentration ratio C obtained will be a function of the distance d; the closer this plan will be to the

  refractor R plus the concentration ratio will be low.

  The refractor A, in accordance with the present invention, is composed, as already indicated, of right prisms p, or,

  more precisely, of two types of such prisms p of which each

  cune has its own geometric characteristics.

  The two sets of prisms are attached to each other.

  be along an appropriate Q junction line and are soli-

  darisés from each other by means, for example, a

  che flat support whose thickness eo does not have an im-

  decisive lift in terms of optical performance

of the device.

  The arrangement, the dimensions (height e, width 1, thickness h) (Fig l, la) and the number of the various prisms

  straight p arranged above and below the rush line-

  tion Q (see Figs 1 to 3) are such that a re-

  fractor R capable of limiting the excursion of the i

  concentrated solar mage, due to the apparent movement of the sun, in a particular plane (the maximum concentration plane Pmc) More particularly, the arrangement of the prisms p must be such that, if we consider two prismatic elements ps

  located above the junction line Q and pi located above

  under said junction line, which are arranged so

  to capture incident solar radiation at equi-

  distant (by a distance yi) from said line, the inferior element

  laughter pi must always have a "focal distance" f smaller

  tite that the focal length f 'of the upper element ps

(Fig 2).

  The relationship between the focal length of the element

  furthest from the junction line U and it

  the upper element farthest from said line is always

days less than 1.

  The "focal distance" of a prism p for a given radius and a given position of the prism is defined as

  distance between the flat face of the refractor R and the point of

  intersection of the straight line passing through the rush line-

  tion Q and the outermost radius transmitted by the prism p

  when the angle of incidence on the flat face is zero.

  If we refer to Fig 1, we can see that, in the case of elements with a maximum height e equal to 3 mm, the rays of the sun at eight o'clock on June 22 at a latitude of 42 N , are totally reflected by pi prisms of width 11 equal to 4 mm, arranged in the lower region of the refractor R, and by prisms ps of width 12 equal to

  13 mm or less, arranged in the upper part of the refractor

  tor. The above results are obtained by positioning

  the flat surface of the refractor R perpendicular to the di-

  rection of the rays of the sun at noon, with an orientation East-

  Where is. In Fig 3 we have designated by X the angle made by the axis of the refracted rays with a horizontal plane T.

  More particularly, the prismatic element is given

  that lower pi a minimum width of 4 mm while one

  gives the upper element ps a minimum width of 6.5 mm.

  These extreme elements produce total reflection for a short period of time after eight hours and by

  Consequently, optimal operating conditions are obtained.

  with a small initial loss of energy.

  After giving the upper and lower elements

  the minimum width 1 determined, we have dimensioned by tang

  the intermediate prisms p so as to have the maximum concentration C in a given plane which was located, as a first approximation, at a distance d = 350 mm from the flat face of the refractor R. The lower part of the refractor R (see again Fig 1) is much larger than the upper part; in this example, there are 42 prisms p, of variable width 1

  in the lower part and 9 p prisms, width 1 va-

riable, in the upper part.

  The refractor R according to the invention can be made of any transparent material Suppose, for example, that such a

  material used has a refractive index of 1.5; the re-

  fractor R will have the ability to concentrate and limit the ex-

  cursion of the image of the sun so as to obtain the following concentration ratio during the period going from 8 hours to 16 hours: L C Lt 2.60 (see Figp 3 to 6) on a plane of maximum concentration located at a distance

d = 358 mm.

  Fig 4 shows that the concentration ratio varies when we go from d = 358 mm to d = O. Regarding the energy loss by the outermost elements which cause total reflection, we can calculate that this energy loss is only 1.5 X of the refracted energy during the period from 8 to 16

hours.

  Fig 5 is a graphic representation of the image of the sun as it appears in the plane of concentration

maximum Pmc.

  The reference R designates the contour of the refractor while the references La, Lb, Lc, Ld, Le, designate the contours of the image of the sun during the period from 8 hours to

  12 hours, it is easy to deduce the concentration report

tion C = L. The

  We did not represent the images of the sun during the

  near noon since these images correspond to those of the respective hours of the morning which are "symmetrical", compared to 12 hours and that they are symmetrical to these images

  in the morning compared to the median plane of the refractor.

  By calculation, it was found that the maximum concentration plane, F Pmc, is located at a distance slightly different from that initially admitted, that is to say that the distance

d = 358 mm.

  Indeed, in Fig 6, the y axis represents the plane along which the prismatic elements are staggered (Fig l)

  while the x-axis represents the distance d; the radius

  rs is the radius refracted at 12 o'clock by the edge ex-

  térieur of the 9 th upper element and the lower ray ri is the refracted ray, also at 12 o'clock, by the outer edge of the 42 th lower element, while the line rin represents the intermediate radius refracted by the 2 nd element

more than 8 hours.

  The intersection of the ri and rin rays gives the exact position of the maximum concentration plane Pmc which is located at: d = 358.34 mm In this plane and during the period which goes from 8 hours to 16 hours, the maximum and minimum coordinates rays transmitted on the y axis are the following Y max = 118.14 mm Y min = 53.52 mm so that the following concentration ratio is obtained:

= 118.14 + 53.52 = 2.60

  equation in which 447 is the total width, in millimeters-

  very, of the 53 prismatic elements p which determine the lar-

  geur L of the refractor R of the example.

  The refractor R of the invention can be manufactured with a thickness e + eo of only a few millimeters; therefore, it may be lighter than known refractors

  and have high performance with regard to trans-

energy mission.

  Consequently, it can be concluded that the refractor which is the subject of the invention is easier to manufacture and more convenient to use than known refractors; in

  in addition, its performance is superior.

  Naturally, these features add to the new

  vel advantage which is to concentrate energy without the use of

  mechanisms that follow the apparent position of the sun.

Claims (9)

R E V E N D I C A T I O N S   1 refractor made of a transparent material designed to remain in a fixed position over time, characterized in that it comprises afocal structural elements arranged asymmetrically with respect to a junction line (Q) in fa-   how to get a solar energy concentration report   re (C) greater than or equal to 2.6 during the period from 8 a.m. to 4 p.m.   2 Refractor according to claim 1, characterized in that the afocal structural elements are stepped straight prisms (p) each of which has appropriate dimensions   and which are formed in one piece with a material support   transparent material of any thickness (eo).   3 Refractor according to any one of the claims   1 and 2, characterized in that the afocal structural elements are straight prisms having a maximum height (e) equal to 3 mm and a width (1) equal or greater than 4 mm   in the lower part of the refractor, and equal or superior-   re at 6.5 mm in the upper part of the refractor, the   position being such that the maximum concentration ratio (C) can be reached in a plane (Pmc) located at a distance   about 350 mm from the refractor (R).   4 Refractor according to any one of the claims   1 to 3, characterized in that the structural elements   afocal are prisms (p) whose crenellated faces are re-   clad in appropriate reflective layers designed to minimize dispersion by the user device, the   refractor (R) forms the cover.   Refractor according to any one of Claims 1 to 4, characterized in that the extreme structural elements (pi, ps) produce total reflection during a short period of time.   6 Refractor according to any of the claims   previous tions, caract 6 laughed in that the sup elements 6-   laughing with respect to the junction line (Q) are always   in smaller numbers than the lower 6 elements.   7 Refractor according to claim 6, characterized in that the prismatic elements which are higher by   compared to the junction line (Q) are 9, tan-   say that the elements which are inferior compared to said   there are 42 connecting lines.   8 Refractor according to any one of the claims   tions above, characterized in that the ratio between the focal length of the lower most pointed element 161 of the junction line (Q) and that of the upper most   far from said line is always less than 1.   9 Refractor according to any one of the claims   tions above, characterized in that it forms a modular type element which can be assembled at will to one or   several other identical elements.